Free movement of solutes between different portions of the extracellular space in the eye is inhibited by the presence of anatomic and physiologic permeability barriers. The purpose of this project is to establish the ultrastructural location of these anatomic barriers and to preserve the ocular effect of altering barrier permeability. This will be done by visualizing the flow of a variety of peroxidase tracers in the electron microscope. After the normal pattern of tracer flow is established in different portions of the eye, a variety of techniques will be used in an attempt to alter the permeability of the barriers described. The principal experimental animals are primates.